Polycarbonate resins are widely utilized as materials for OA appliances, electric and electronic components, domestic appliances, construction parts, automobile parts, etc. because of their excellent impact resistance, heat resistance and electric characteristics. While polycarbonate resins have a higher flame retardancy as compared with polystyrene resins, much higher flame retardancy is required when used in the field of, particularly, OA appliances and electric and electronic components. In such a utilization, various flame retardants are added to the polycarbonate resins to improve the flame retardancy.
For example, organic halogen compounds and organic phosphorus compounds have been hitherto added. Most of these flame retardants, however, have a problem of their toxicity. In particular, organic halogen compounds have a problem that a corrosive gas is generated upon combustion. In this circumstance, there has been an increasing demand for imparting flame retardancy using non-halogen and non-phosphorus flame retardants in recent years.
As non-halogen type or non-phosphorus type flame retardants, various proposals have been made to use polyorganosiloxane compounds.
For example, Patent Document 1 discloses a flame retardant resin composition containing a thermoplastic resin and compounded therein a polyorganosiloxane-containing graft copolymer obtained by graft polymerizing a vinyl monomer to polyorganosiloxane particles of 0.2 μm or less. The flame retardant resin composition, however, has a problem that the balance between the flame retardancy and impact resistance is not good. Namely, while the impact resistance thereof is satisfactory to some degree, the flame retardancy thereof is insufficient.
In an attempt to solve the problem of Patent Document 1, Patent Document 2 proposes a polyorganosiloxane-containing graft copolymer obtainable by polymerizing (B) a polyfunctional monomer and a copolymerizable monomer other than the polyfunctional monomer in the presence of (A) polyorganosiloxane particles, and by further polymerizing (C) a vinyl monomer. A resin composition having excellent flame retardancy and impact resistance is disclosed to be obtainable by compounding the graft copolymer into a thermoplastic resin.
The polyorganosiloxane particles (A) contained in the graft copolymer have an average particle diameter of 0.008 to 0.6 μm. Such particles, when compounded in a polycarbonate resin, form aggregates of about 3 μm because of poor dispersibility. Therefore, the desired flame retardancy is not obtainable. Additionally, the proposed resin composition has a problem that the flame retardancy and the like properties of products obtained therefrom vary product to product.
Patent Document 3 discloses a resin composition which is attempted to improve the transparency and which contains a polycarbonate resin, an alkali metal salt of a perfluoroalkanesulfonic acid and a bisphenol type epoxy resin. The flame retardancy of the resin composition is, however, unsatisfactory, though the transparency is improved to some degree.
[Patent Document 1] JP-A-2000-264935
[Patent Document 2] JP-A-2003-238639
[Patent Document 3] JP-A-Hei 6 (1994)-73281